An Aiúa was an intelligent philote. Philotes have varying degrees of "cleverness" or "willpower", which describes their ability to control other philotes and enforce upon them a pattern. Philotes that are strong enough to govern the pattern of an entire person are called aiúa. Sapient creatures consisted of uncounted numbers of "dumb" philotes governed by one Aiùa, which held the collection together and could have been thought of as the physical representation of the soul.[1]
When a sapient creature dies, its philotes retain their connectivity for some amount of time, proportional to the complexity of their pattern. Gradually, they revert to being governed by the dominant philote in the area, usually the philote governing the planet the creature was on.[1]
When a sapient creature is born, its body is an "empty pattern". The body "calls" for an aiúa that is compatible with its pattern, and since the Outside is full of infinite philotes, a matching aiúa will appear and assume control.[1]
According to Grego Ribeira, the term was inspired by the Sanskrit word for 'life,' likely "āyus."[1]
The first time aiúas were mentioned was when Ela Ribiera, Andrew Wiggin, and Miro Ribeira were trying to get to the Outside; a region outside of the universe that contained an infinite number of Aiùas.[1]
Formic Hive Queens had the ability to see Aiùas, and see how powerful or "bright" they were. The Hive Queen of Shakespeare explained that one did not have an Aiúa, one was an Aiúa, and that all creatures capable of movement were one at a fairly high level.[2]